Sliding-type variable resistor having thin film resistor layer comprising strap resistors

ABSTRACT

The sliding-type variable resistor including thin film strap resistor layers formed by vacuum deposition, spattering, etc. upon an insulating material base, a plurality of tap electrodes and a sliding brush slidable thereover. Tap electrodes are arranged in the path of travel of the brush and extended in one direction from the path. Strap resistors are arranged with the same pitch as that of the tap electrodes and one end of the resistor overlays on the extended portion of the corresponding tap electrode. Each strap resistor overlays on the ends of two strap connectors, and each strap connector overlays on two adjacent strap resistors.

United States Patent Inventors Tatsuo Fujii Tokyo; Yutaka Watano. T okyo: Masaaki Tsukamoto, Kawmki-shi, allot, Japan App]. No 4,987 Filed Jan. 22, I970 Patented July 20, I971 Assignee Nippon Kogaku K. K.

Tokyo, Japan Priority Jan. 31, 1969 Japan 42/7905 SLIDING-TYPE VARIABLE RESISTOR HAVING THIN FILM RESISTOR LAYER COMPRISING STRAP RESISTORS [56] References Cited UNlTED STATES PATENTS 2,632,831 3/1953 Pritikin 338/140 2,717,942 8/1955 Andrews 338/89 X 2,878,357 3/1959 Thomson .4 338/295 X Primary E raminer-Lewis H. Myers Assistant Examiner-Gerald P. Tolin Attarneyward, McElhannon, Brooks & Fitzpatrick ABSTRACT: The sliding-type variable resistor including thin film strap resistor layers formed by vacuum deposition, spattering, etc. upon an insulating material base, a plurality of tap electrodes and a sliding brush slidable thereover. Tap electrodes are arranged in the path of travel of the brush and extended in one direction from the path. Strap resistors are arranged with the same pitch as that of the tap electrodes and one end of the resistor overlays on the extended portion of the corresponding tap electrode. Each strap resistor overlays on the ends of two strap connectors, and each strap connector overlays on two adjacent strap resistors.

PATENTEDJUL20197| 3,594,686 SHEET 1 OF 2 "-3 n-Zkl 0/ [HI/4.

INVENTORS TA TSUO FUJII By YUTAKA WATANO MASAAKL TSUKAMOTO had, 2 wow, [2% p 2 7M SLIDING-TYPE VARIABLE RESISTOR HAVING TIIIN FILM RESISTOR LAYER COMPRISING STRAP RESISTORS This invention relates to a variable resistor and more particular to thin film resistor layers and electrodes of the variable resistor.

An object of the present invention is to provide a variable resistor having thin resistor layers in which the stepped resistor layer section is provided so that the high resistance which has been so far unattainable by the conventional variable resistor can be obtained. The error caused by the misalignment of the mask patterns used in the vacuum deposition of the resistor layers, etc. may be minimized.

To this stepped resistor layer section is further connected a zigzag resistor section, so that one resistor layer may cover a wide range of resistance up to a very high resistance.

In brief, according to the present invention, a pattern is employed which permits one resistor layer to cover a wide range of resistance in the direction perpendicular to the path of travel of a sliding brush of an adjustable registor. Furthermore, it is possible to minimize the error in resistance caused by the misalignment of the mask for forming tap electrodes with the mask for forming resistor layer and by the tolerances of the manufacture of the patterns. Therefore, an adjustable registor with a higher degree of precision which can vary its resistance in accordance with a given function may be provided at a less expense with a high yield.

The objects, advantages and features of this invention will be described in detail referring to accompanied drawing, in which:

FIG. 1 is a plan view of thin film resistor layers of a conventional sliding-type variable resistor;

FIG. 2 is a plan view of one embodiment of the present invention;

FIG. 3 is for explanation of the correction is resistance in a step manner in accordance with the present invention;

FIGS. 4 and 5 are fragmentary plan views of the conventional resistors for explanation of the defects thereof; and

FIG. 6 is a view similar to FIG. 3 for explanation of the correction in resistance in a step manner in accordance with the present invention.

As shown in FIG. 1, in the conventional electrode and resistor layers formed through the masks by vacuum deposition, spattering, etc., the tap electrodes I are formed at right angles relative to the path of the sliding brush and a wedge-shaped resistor layer 2 which is tapered in accordance with a function is overlaid upon the tap electrodes .1. Another resistor layer 3 is located so as to extend from the tip end of the wedge-shaped resistor layer 2. The tip end of the resistor layer 2 has the width as minimum as possible in the fabrication technique and the resistor layer 3 has a resistance per unit of area (surface resistance) higher than that of the resistor layer 2. When a range of resistance is widened in one resistor layer as described above; the base width S of the resistor layer must be increased, but is limited in practice. Therefore, a number of deposition operations must be increased disregarding the increase in cost. 1

There has been proposed another method in which as shown in FIG. 4 the zigzag resistor members are connected in series with the wedge-shaped resistor layers. However, when the pitch of the tap electrodes is limited, there is a defect that the relative error are increased because of the distortion of the pattern as shown in FIG. 5.

The present invention contemplates to eliminate the defects of the conventional adjustable resistor of the type described.

In FIG. 2, reference numerals 4, 4' and 4" designate tap electrodes which contact with a sliding brush and are made of a material having a low shut resistance, a strong resistance to abrasive wear and a property for ensuring a better electrical contact with the sliding brush. Reference numerals 5 and 5 designate connecting straps made of same material as the electrodes. and formed by the vacuum deposition simultaneously with the formation of the tap electrodes 4, 4 and 4" by use of. the same mask. That is, the same or common mask is provided with slots for forming the tape electrodes 4, 4' and 4" and the slots for forming the connecting straps 5 and 5'. A resistance layer 6 has a relatively high sheet resistance and a wedge shape generally indicated by P whose width S is so varied as to provide a variation in resistance in accordance with a given function. (Such a resistor will be referred to as function resistor hereinafter for brevity.) Strap resistors 7 are formed simultaneously with the resistor layer 6 and arranged in sideby-side relation with the tap electrodes 4' with the same pitch therewith. The tap electrodes 4 and the strap resistors 7 are overlapped at the outside of the path K of the slidingbrush, and the width of the tap electrode 4' is made wider than that of the corresponding strap resistor 7. The strap resistors 7 are also formed simultaneously with the resistor layer 6 and the strap resistor 7 and arranged so that two strap resistors 7' are provided for every one of the tap electrodes 4-".

The strap connectors 5 are overlaid with two strap resistors respectively in the stepped resistor section Q and one of the strap connectors 5 is connected to the strap resistor formed adjacent to the lower resistor layer. The strap connectors 5 are overlaid with all of the strap resistors 7' in the zigzag resistor section R. That is, the adjacent strap resistors which are not connected to a common tap electrode 4"v are bridged by the strap connector 5'.

Reference numeral 9 designates an electrically insulating 7 base and is provided with a notch 10a at one portion of the outer periphery 8 thereof at the intermediate of the zigzag resistor section R so that the strap resistors in the zigzag resistor section, the tap electrodes and the strap connectors are not overlapped one upon another when vacuum deposited. Reference numeral 10 is a pin which serves to determine the reference position in case of the vacuum deposition, of the resistance layers, and tap electrodes upon the base 9, by abutting the pin 10 against one side edge of the notch l0a of the base 9.

The sliding brush generally indicated by J is comprised of contacts .I I, J2, J3 and J4 and adapted to slide over the path K. It is noted that the contacts are not arranged in line as shown in FIG. 2 so that the contactor as a whole may contact with more than two tap electrodes.

Next the mode of operation will be described. Assume that the wedge-shaped resistor layer 6 increases its resistance in logarithmic manner. In this case, the width 8' of the resistor is gradually decreased and reaches the limit of fabrication or desposition. In this case, the resistance is in proportion to the distance from the terminal N, which is considered as the reference point, but in inverse proportion to the width. Therefore, when the width of each resistor is made constant and the resistors are arranged and connected as shown in the sections Q and R in FIG. 2, it is possible to obtain a higher resistance than the wedge-shaped resistor within a limited space. The step resistor section Q is interposed between the wedgeshaped resistor 6 and the zigzag resistor section R so that the abnormal resistance caused, as shown at b and g in FIG. 5, by the misaligned depositions between the tap electrode 4" and the strap resistor 7" and between the strap connector 5" and the strap resistor 7", can be prevented. That is, as shown in FIG. 4, inthe zigzag resistor section R, two strap resistors 7 are connected to one tap electrode 4" in spaced-apart relation by a distance i, and the tolerance e between the strap connector 5 and the strap resistor 7' and the tolerance c between the tap 4" and the strap resistor 7' must be provided within a limited space and pitch, so that these tolerances cannot be made larger. Furthermore, the width f of the strap connector 5' cannot be made wider because of the spacing 1'. Therefore in the vacuum deposition step, the position of the base 9 is determined by fitting the reference pin 10 into the notch 10a, but as long as the taps 4", the strap connector 5' and the strap resistor 7' are deposited individually, the errors in their relative positions are inevitably caused. Therefore, as shown in FIG. 5, the deviations are caused between the tap 4" and the strap resistor 7 and between the latter and the strap connector 5" so that the abnormal resistances appear at the portions 5a" and 5b" because of the nonuniform current flow through these positions. Especially in the low resistance section the abnormal resistance in excess of the permissible tolerance cannot be disregarded at all.

In order to prevent the above-described defect, the zigzag resistor section R having such a high resistance that the abnorrnal resistance as described above may be negligible is providedand between the wedge-shaped resistor layer 6 and the zigzag resistor section R is interposed the step resistor section as shown in FIG. 3. The increment in length of the strap re sistor relative to the increment in resistance between the adjacent taps is relatively small as compared to that in the section R so that only one strap resistor is enough for each of the taps. Therefore, the tolerances a and a between the tap 4' and the strap resistor 7, the tolerance d between the strap connector and the strap resistor -7 and the spacings hand h may be made larger so that even when the relative position between the tap and the strap resistor is slightly deviated from their correct positions, the abnormal resistances appeared in the position b and g in FIG. 5 may be prevented. Thus, the abnormal resistance in the zigzag section R can be eliminated.

From the standpoint of the present state of the vacuum deposition, the spacing S as well as the width W of the strap connector are limited so that when the increment (Y-Y') in length of the strap resistor Y relative to the increment in resistance between the two adjacent taps isless than the sum of S and-W, the lower edge 4b of the tap 4' is located at the position Z which is spaced apart from the reference line X-X' by a distance of (cl-A2), whereAz =(the sum of s and w) (Y'-Y). Therefore, in order to that the step resistor section 0 may be arranged over a relatively wide area within a limited space, the distance z must be reduced as much as possible. For this purpose, as shown in FIG. 6, the strap connector 50' to be connected to the, tap it is vacuum deposited at a position spaced apart from the strap connector 50 upwardly by a distance of Y. In this case, the distance Y must be so selected I that the spacing between the strap connector 5c between the strap resistors connected to the taps n-3 and n-2 and the strap connector 5a" may become larger than the minimum permissible spacing which is allowed in preparation of the vacuum deposition masks. Therefore, the increment in length A Yn between the strap resistors connected to the taps n-l and n relative to the increment in resistance Rn between the two adjacent taps n-l and n when the strap connector 5a is not deposited at the raised position and when the resistance of the tap is negligible.

. (Ynrl'S)-YnI=-An However, when the strap connector 50' is raised by the distance Y to the position indicated by 5a, the distance from the strap resistor 7 through the strap connector 50' to the tap n is shorter than that through the strap connector 511". Therefore, in under to retain the increment AYn, the length Zn of the tap n is shortened so that the lower end of the tap may be located at the position indicated by 4b. In this case, the length of the new strap resistor for the tap it and the length of the tap Regarding (tr-l) tap, the strap connector 5a" is placed between the electrode 4a" and the strap connector 5a so that the distance Y, is reduced by the width W, so that the distance 2,, should also be reduced by W for securing l namely,

The value of y is limited by the distance Z from the reference line X-X' and is given from equation (l) In order to prevent the overlapping between the adjacent strap n become Y'n and Z'n respectively. Inthis case, the decreis: AZn=[( Yn-y-W-SlH? W)}[ Yn+S1 -2( WH-S) (l Thus, it is seen that the length Zn may be shortened by 2( W+S irrespective of the distance y. That is, new length Yn and Z'n are given by the following relations:

Zn'=Zn-2( W-l-S) (2) and connectors 50" and 5c and provide a spacing larger than S in the direction of the strap resistor in view of the tolerance required in the preparation of the mask for vacuum deposition, the value of y is 1 YZH In order that the strap connector 5a may be spaced apart from the lower end 4b of the tap 4a by a distance more than it i I .Y'n That is, from equation (3),

Ynrl-W y (6) Therefore, from equations (5 and (6),

- new; 2 m+'s Yr: 2 ZSrl-W In order that the con tap (n-l by a distance longer than S,

' u We .2 S

Y,, .,+Ws y 7 From equations (5) and (7),

a ew-s; y g 2 was Hence I, :BSH-W (8) That is, when the equations (4), (5), (6').and (8) are'satisfied, thestrap connector may be repeated as many as times required so that the steplike resistor may be arranged effectively in a limited space so that a wide and stable resistance range maybe provided.

In order to provide a sufficient spacing f in FIG. 4, the strap connectors may be arranged slantingly as indicated by dotted lines 11 and 12 in FIG. 2.

From theforegoing, it is seen that oneresistor layer may provide a wide range of resistance with less relative error in a limited space. Even though the arrangement is such that the two adjacent tap electrodes are interconnected by the strap resistor layer extending radially, the influence b the misalignment between the tap electrode and the strap resistor may be remarkably minimized. Therefore, the adjustable resistor whose resistance may be varied in accordance with a given function may be provided at a low cost with a higher degree of accuracy.

From the construction of the present invention, the follow ing advantages may be accrued:

1. In the step resistor section, the lengths of the strap resistors may be reduced in the lower resistance side so that the errors in width of the strap resistors may be reduced. Therefore, the relative error in resistance in the lower resistance side may be minimized.

2. The spacing between the strap connectors, that is the dimensions of the bridging portion of the mask may be sufficiently provided without causing any difficulty in fabrication. Furthermore, the pitch can be made smaller.

3. More space in the mask may be utilized and a life thereof may be increased. The mask alignment tolerance may be increased. v

4. The types of the resistor layers may be reduced so that a number of vacuum deposition may be reduced, thereby preventing the superposition of various errors in vacuum deposition. Thus better quality and low-cost precision resistors may be provided.

What we claim is:

l. A variable resistor comprising thin film resistor layers formed upon an insulating base, a plurality of tap electrodes and a sliding brush for slidable movement over said tap electrodes, an'improvement resides in that strap-shaped tap elecnector 50" may be spaced apart from the trodes (4) arranged in side-by-side relation in the path of travel of said sliding brush are extended in one direction out of said path;

tively, the width of each of said smaller than that of each of said tap the sheet resistance of each of said st strap resistors being electrodes; rap resistors is higher than that of each of said tap electrodes each of said strap resistors is overlaid with ends of two strap connectors (5), one of said two straps being connected to the adjacent strap resistor on the lower resistance side while the other,

to the adjacent strap resistor on the higher resistance side; and

each of said strap connectors is overlaid only upon the two adjacent strap resistors.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 p 594, 686 Dated July 20th, 1971 Inventoz-(s) AL It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 3, line 61, change" (n" to (n-2) Column 4, line 3, change "Yn11" to Y line 4, change "Z1 1" to Z 1 same line, change "Y to Y line 6, change "Z1111" to Z 1 line 10, change "Z1 to 0 Signed and sealed this 9th day of May 1972.

(SEAL) Attest:

EDWARD M.FLETCHER, JR. ROBERT GOT'ISCHALK Attesting Officer Co missioner of Patents FORM PO-IOSO (IO-69) USCQMM DC 603764369 u.s sovznmvlsm PRINTING omc: 1 sun o-aes-au 

1. A variable resistor comprising thin film resistor layers formed upon an insulating base, a plurality of tap electrodes and a sliding brush for slidable movement over said tap electrodes, an improvement resides in that strap-shaped tap electrodes (4'') arranged in side-by-side relation in the path of travel of said sliding brush are extended in one direction out of said path; strap resistors (7) arranged side-by-side relation with the same pitch with that of said tap electrodes and in the one-to-one relation therewith have their one ends overlaid upon said extended portions of said tap electrodes respectively, the width of each of said strap resistors being smaller than that of each of said tap electrodes; the sheet resistance of each of said strap resistors is higher than that of each of said tap electrodes each of said strap resistors is overlaid with enDs of two strap connectors (5), one of said two straps being connected to the adjacent strap resistor on the lower resistance side while the other, to the adjacent strap resistor on the higher resistance side; and each of said strap connectors is overlaid only upon the two adjacent strap resistors. 